The mechanics of head movements will be examined in parallel with single unit studies of the sensory-motor integration of head movements in cat. The action across the cranio-cervical joints of individual muscles moving the head will be examined, and an attempt will be made to identify a pattern generator controlling the synergism or co-contraction of many neck muscles which move the head about individual axes; these individual muscle actions form a vector (angle and amplitude) representing a given movement. The identification of the pattern generator will be facilitated by stimulating the superior colliculus, in which topographic representation of head movement vectors exists, and comparing the resulting patterns of muscle activity and head movement with those obtained from semicircular canal actions (elicited by natural stimulation), optokinetic stimulation, and voluntary head movements. These studies are a necessary prerequisite for the analysis of sensory-motor coordination as it relates to head movements. The number of degrees of freedom in the relationship of head movement to neck muscle activity will be reduced to facilitate assessment of individual muscle contribution to overall head movements and the relationship of individual muscle patterns of activity and head movement to single unit activity. Single units will be recorded in the vestibular and underlying reticular formation during stereotyped eye and head movements. Cats are trained in an eye-head movement task which produces patterned and repeatable movements that allow characterization and quantification of vestibular, neck proprioceptor, and visual sensory and motor nervous signals relevant to the generation of head movements; normal patterns of motor control of reflexly- and voluntarily- generated head movements are examined in this model. Single neurons will be examined for their contribution to the generation of head movements and for the integration of vestibular and neck sensory signals in the reflex control of head movements. Taken together, studies of head movement mechanics and single unit activity will examine the mechanisms of muscular contractions in the control of head movements, and correlates to neurological disease in humans will be sought.